When an abnormality occurs, for example, when a current excessively flows through an electrical apparatus (for example, a motor) and thereby causes the electrical apparatus to leach an abnormally high temperature or when the electrical apparatus reaches an abnormally high temperature due to some reason other than the excessive current, it is needed to secure a safety of the electrical apparatus by interrupting the current flowing through the electrical apparatus and eliminating the abnormality when necessary. A bimetal component is used as a means to interrupt the current as described above.
The bimetal component comprises a sheet member of a bimetal metal. The bimetal component is configured to be activated (i.e. deformed) so as to interrupt a current flowing through the bimetal component when the bimetal component itself reaches a higher temperature in excess of a predetermined temperature, or when the bimetal component reaches a higher temperature in excess of a predetermined temperature due to arise in the temperature of an ambient atmosphere of the bimetal component.
When such bimetal component is incorporated in an electrical apparatus, it is activated when the electrical apparatus leaches an abnormal temperature clue to an excessive current or some other reason, so that the current is ink. The temperature of the electrical apparatus decreases by the interruption of the current. Since the temperature of the bimetal component also decreases, the bimetal component returns to its original shape (i.e. it recovers), as a result of which the current may be allowed to flow again before the safety of the electrical apparatus is secured.
In order to prevent the current from flowing again as described above, it is necessary to ensure and maintain the state when the bimetal are activated. For this purpose, the bimetal component is disposed in series in a circuit of the electrical apparatus so that it can interrupt the circuit current, while at the same time a PTC component is disposed in parallel to the bimetal component. By such arrangement, when the bimetal component is activated, the current flowing through it is diverted to the PTC component the PTC component generates a Joule heat by the current and this heat is transmitted to the bimetal component so that the activated state of the bimetal component can be ensured.
A protection device is known which is configured so that a movable contact which is operated by the bimetal component is disposed in series in the electrical circuit and the PTC component is disposed in parallel to the bimetal component as described above. Such a protection device is disclosed, for example, in Patent Reference 1 shown below. In such a protection device, a resin base having a terminal comprises a PTC component, a bimetal component and an arm within a space provided in the resin base; a cover which is previously provided with an upper plate is placed on the resin base, and the resin base and the resin cover in this state are bonded with an adhesive or by ultrasonic fusion to form a resin housing. In such protection device, the terminal and the atm protrude from the resin housing.
JP-A 2005-203277 is a prior patent reference.